1. Field of the Invention
This invention relates to a novel method of coating a substrate with a chip-resistant nondiscoloring polyurethane protective coating containing pigmented acrylic lacquer, acrylic enamel, or nitrocellulose lacquer.
2. Background of the Prior Art
Notwithstanding a considerable portion of roadways being paved, both in the United States and in foreign countries, there exists a serious paint chipping problem which continues to plague motor vehicle owners, caused by gravel and other small particles on the road bed being thrown against the painted surfaces of such vehicles. The same problem plagues the owners of other painted structures such as boats, trailers, airplanes, trains, tanks, towers, and the like, although the impacting particles may be from other sources.
The chipping problem is perhaps most noted by the owners and manufacturers of automobiles, particularly those having the so-called European body style wherein the body of the automobile tends to curve inwardly immediately behind the front and/or rear wheels. This situation causes particles such as gravel from streets and other roadway surfaces to be carried on the surface of the tires and impacted against the painted surface of the automobile. Since the paved roadways typically have small gravel particles and other hard particles on their surface and unpaved roads usually always contain such material, the propelling of high speed particulate material against the painted surface of the automobile is unavoidable. While means have been suggested for imposing a shield such as a mud flap or mud guard between the automobile wheel and the painted surface, this solution has not been completely satisfactory because it detracts from the vehicle's aesthetic appearance and adds yet another cost to the already high price of the automobile.
Attempts have been made to produce tougher, more chip-resistant paint for automobiles, but these have not been generally completely satisfactory. Polyurethanes have been employed in paint compositions in an attempt to make the paints tougher and more durable, but there has been some difficulty in pigmenting the polyurethane protective coating to make it indistinguishable from existing paints already applied to the automobile. This presents a serious problem in automobiles since, because of its higher cost, polyurethanes are typically not employed to cover the entire surface to be painted. Rather, the chip-resistant coatings are cusotmarily added to those locations which would be more susceptible to chipping, e.g., on the automobile body immediately behind the wheels, the leading portion of the automobile such as the front of the hood and other front portions of the body.
Vinyl plastisols are being employed as chip-resistant coatings. The heat such coatings require for curing dictates their use before painting in the manufacturing plant virtually precluding their use in repair shops because such heating would damage existing painted surfaces. Such repair shops typically use a vinyl composition which air dries. Such coatings are also not particularly desirable because they are generally rough and inconsistently textured and difficult to repair. Additionally, a commercially available polyurethane enamel sold under the registered trademark "Imron" has been available as a chip-resistant protective coating, but it has only a moderate degree of chip-resistance and it is not recommended for blending with known pigmented lacquers or enamels.
U.S. Pat. No. 3,401,143 by Finelli and West discloses one example of a pigmented polyurethane protective coating which may be blended with commercial pigmented lacquers, such as acrylic resin, vinyl acrylic resin and nitrocellulose lacquers. But such polyurethane resins are not suited for use in a broad spectrum of commercial pigmented lacquers, including acrylic enamels, because of the presence of certain diamine catalysts. In fact, blends of such polyurethane and pigmented acrylic enamel produce a liquid composition which, when applied to a surface, dries to a rough unsightly finish.
Automobile repairmen and dealers desire a liquid composition which will provide an inconspicuous protective coating which is non-sagging and compatible with all of the more commonly used pigmented paints including acrylic enamels and other paints such as acrylic lacquer and nitrocellulose lacquer. The present invention provides such a composition.